1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display, and more particularly, to an organic light emitting diode display having a heating circuit structure for directly forming pixels having different colors by utilizing a heating process.
2. Description of the Prior Art
In various types of flat panel displays, since an OLED display, being developed later than a liquid crystal display (LCD), has many beneficial characteristics, such as having a spontaneous light source, a wide viewing angle, high response velocity, power saving, strong contrast, high brightness, small thickness, full-color, simpler structure, and a wide operating temperature, the OLED display has been used extensively in small and medium scale portable display fields. After continuous research and development by manufacturers and scholars, breakthroughs on some unresolved problems, such as low yield rate, unsatisfied mask application, unstable cap seal, there has been significant progress. In the future, the OLED will probably even be used in the large-size display field.
When analyzing the future development of the organic light emitting diode display, it is very important to realize the driving method of an OLED display. The OLED display is an electrically driven lighting element having a brightness that depends on the magnitude of a related current. At present, the magnitude of the brightness (which is also called the gray-scale value) is controlled by the magnitude of the OLED driving current in an application of OLED matrix display. Based upon the driving method, the matrix display can be classified as either a passive matrix display or an active matrix display. Passive matrix displays adopt the method of driving the scan lines of the display in sequence, driving pixels in different rows sequentially. Since the light-emitting time of each pixel is restricted by the scanning frequency and the numbers of scan lines, the passive matrix method is not suitable for large-size and high resolution (when the number of the scan lines is increased) displays.
Active matrix displays, however, possess an independent pixel circuit for each pixel, which includes a capacitor (C), an OLED light-emitting component, and at least two thin-film transistors (TFTs) that are used to adjust the OLED driving current. With this arrangement, even in large-size and high resolution displays, a steady driving current is provided to each pixel, which improves the brightness balance.
Similar to other types of displays, when an OLED display is used to realize colored images, red light beams, green light beams, and blue light beams need to be formed first. Conventionally, materials for generating white light beams are utilized. White light beams then pass through red, green, and blue light filters for transforming the white light beams into colored light beams. However, color filters need to be used in this method. Under the circumstances, the alignment accuracy needs to be controlled to maintain the balance of the colored light beams, leading to limitation in layout. Consequently, the aperture ratio is reduced.
In another frequently adopted conventional method, different materials are utilized to form red pixels, blue pixels, and green pixels. The red pixel, the blue pixel, and the green pixel then make a colored pixel such that the red light beams, the blue light beams, and the green light beams are mixed. Please refer to FIG. 1. FIG. 1 is a schematic diagram of a conventional OLED panel 10 formed by three different colored pixels. As shown in FIG. 1, the conventional OLED panel 10 comprises a transparent substrate 12. The transparent substrate 12 may be a glass substrate, a plastic substrate, or a quartz substrate. A plurality of red pixels 16, blue pixels 18, and green pixels 22, arranged in a matrix, are included on the surface 14 of the transparent substrate 12. The neighboring red pixel 16, blue pixel 18, and green pixel 22 form a colored pixel 24.
Please refer to FIG. 2. FIG. 2 is a cross-sectional diagram of the OLED panel 10 shown in FIG. 1 along line 2–2′. As shown in FIG. 2, each of the pixels 16, 18, 22 (please refer back to FIG. 1) in the OLED panel 10 respectively comprises a transparent conductive layer 26, 28, 32, and each of the transparent conductive layers 26, 28, 32 is formed on the transparent substrate 12 and used as an anode of each of the OLEDs. An organic thin film 34 is formed on the transparent conductive layer 26. An organic thin film 36 is formed on the transparent conductive layer 28. An organic thin film 38 is formed on a surface of the transparent conductive layer 32. A metal layer 42 is respectively formed on a surface of the organic thin film 34, 36, 38, and each of the metal layers 42 is used as a cathode of each of the OLEDs. Since the organic thin films 34, 36, 38, may have different material compositions, thickness, or combinations, each of the pixels 16, 18, 22 in the OLED panel 10 will emit different colored light beams to form the colored pixel 24.
On the other hand, the conventional method, which utilizes materials for generating white light beams and let white light beams pass through red color filters, blue color filters, and green color filters to respectively generate red light beams, blue light beams, and green light beams, tends to cause problems of unsatisfactory alignment accuracy. Not only do the three different colored light beams oftentimes appear unbalanced, but the aperture ratio is also reduced. When utilizing different materials to form the red pixel, the blue pixel, and the green pixel and combining the three different colored pixels as a colored pixel to mix the red light beams, the blue light beams, and the green light beams, a problem of discrepancies in organic thin films in different colored pixels often emerges. Due to the discrepancies in organic thin films in different colored pixels, the processing becomes more complex. Furthermore, the problem of unsatisfactory alignment accuracy and other problems incurred from processing occur when the process control is bad, leading to defects on products.